Study on Hydrogen Induced Delayed Cracking Behavior of Zirconium Alloys Caused by Surface Defects
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摘要: 核反应堆用锆合金构件在服役过程中会发生氢致延迟开裂（HIDC）而失效，构件表面的微缺陷是否会引起HIDC是值得研究的问题。本文采用真空电子束焊接方法制备表面有微缝隙缺陷的样品，以研究这类微缝隙缺陷在400℃过热蒸汽中腐蚀以及在350℃高压水中热循环处理过程中的行为。由于这类缺陷处会形成尖劈状的氧化膜并镶嵌在金属中，在氧化膜前端将形成应力集中和应力梯度区，引起氢的扩散、富集和氢化物析出，即使样品中原先没有残余应力，也没有受到外加应力的作用，也会发生HIDC导致裂纹扩展而开裂。因此，在设计和加工制造核反应堆堆芯中锆合金的各种结构件时，需要重视如何避免锆合金构件表面可能生成这种缺陷的问题。
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关键词:
- 锆合金 /
- 氢化锆 /
- 氢致延迟开裂（HIDC） /
- 表面缺陷 /
- 氧化膜
Abstract: Zirconium alloy components used in nuclear reactors maybe occur to fail due to hydrogen induced delayed cracking (HIDC) during service. Whether the microdefects on the surface of the components will cause HIDC is worth studying. In this paper, samples with microcrack defects on the surface of zirconium alloy were prepared by vacuum electron beam welding method, and the corrosion behavior of these microcrack defects during thermal cycling treatment in high-pressure water at 350℃ after corrosion in superheated steam at 400℃ was studied. As the formation of a wedge-like oxide film embedded in the metal at such defects, a tensile stress concentration and stress gradient zone will be formed at the front end of the wedge-like oxide film, resulting in the diffusion and enrichment of hydrogen, and the precipitation of hydrides. In this case, even if the samples are not subjected to external stress and have no residual stresses, these defects will also cause HIDC, leading to defect extension and cracking. Therefore, when designing and manufacturing various zirconium alloy components used in the nuclear reactor core, attention should be paid to how to avoid such defects formed on the surface of such components. -
图 1 拉伸样品加载不同时间后ZrHx在小孔周边缺口应力集中处的形核和生长（暗场像）
Figure 1. Nucleation and Growth of ZrHx at the Notch around the Hole after Loading the Tensile Stress for Different Time (Dark Field Image)
图 2 样品拉伸时在小孔周边缺口处形成的ZrHx发生开裂以及在裂纹尖端应力集中处重新析出ZrHx的过程
Figure 2. Cracking of ZrHx Formed at the Notch around the Hole and Re-precipitation of ZrHx at the Stress Concentration Zone at the Crack Tip during the Sample Tensile Process
图 3 垂直于板材轧制方向加载160 MPa进行热循环不同次数后对带状ZrHx分布取向的影响
Figure 3. Effect of Loading 160 MPa Tensile Stress Perpendicular to the Plate Rolling Direction on the Distribution Orientation of ZrHx Ribbon after Different Times of Thermal Cycles
图 4 从样品截面上观察裂纹尖端处ZrHx的分布
Figure 4. Distribution of ZrHx at the Crack Tip Showed on the Section of Sample
图 5 复合板侧面结合处形成了特殊形貌尖劈状的氧化膜及其ZrHx的分布
Figure 5. A Special Wedge-like Oxide Film Formed on the Side Surfaces of the Joint Composite Plate and ZrHx Distribution
图 6 样品经400℃过热蒸汽腐蚀200 d后微缺陷端部金属中ZrHx的分布形貌
Figure 6. Morphologies of ZrHx Distribution at the Tip of Micro Defect after 200 Days Corrosion in Superheated Steam at 400℃
图 7 样品经350℃/20次热循环后微缺陷端部的几种典型形貌（抛光后未蚀刻）
Figure 7. Some Typical Morphologies of the Micro Defect Tips of the Samples (not Etched after Polishing) after 20 Thermal Cycles at 350℃
表 1 样品经20次和60次热循环后8处微缺陷缝隙深度的变化（20次/60次）
Table 1. The Changes of Crack Depth of 8 Micro-Defects after 20 and 60 Thermal Cycles of the Samples (20 Times/60 Times)
缝隙编号 1 2 3 4 5 6 7 8 深度变化/mm 0.45/0.58 0.41/0.50 0.49/0.88 0.80/0.95 0.95/1.23 0.48/0.48 0.75/0.81 0.63/0.70 
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